Group-III group-V compound semiconductors (often referred to as III-V compound semiconductors), such as gallium nitride (GaN) and its related alloys, have been under intense research in recent years due to their promising applications in electronic and optoelectronic devices. The large band gap and high electron saturation velocity of many III-V compound semiconductors also make them excellent candidates for applications in high temperature, high voltage, and high-speed power electronics. Particular examples of potential electronic devices employing III-V compound semiconductors include high electron mobility transistor (HEMT) and other heterojunction bipolar transistors.
Epitaxially grown films of the III-V compound semiconductor GaN are used in these devices. Unfortunately, GaN epitaxial films must be grown on substrates other than GaN because it is extremely difficult to obtain GaN bulk crystals due to the high equilibrium pressure of nitrogen at the temperatures typically used to grow bulk crystals. Owing to the lack of feasible bulk growth methods for GaN substrates, GaN is commonly deposited epitaxially on dissimilar substrates such as silicon, SiC and sapphire (Al2O3). Particularly, research is focused on using silicon as the growth substrate for its lower cost as compared to other growth substrates and subsequent processing capabilities. However, the growth of GaN films on silicon substrates is difficult, because silicon substrates have lattice constants and thermal expansion coefficients different than those of GaN. If the difficulties of growing GaN films on silicon substrates could be overcome, silicon substrates would be attractive for GaN growth given their low cost, large diameter, high crystal and surface quality, controllable electrical conductivity, and high thermal conductivity.
Improved methods for forming III-V compound semiconductor devices continue to be sought.